Conventionally, as a method for measuring the pulse rate, there is known a method that detects an electrocardiographic signal that produces a heartbeat. Recently, there has been used a method for measuring the pulse rate (photoelectric sphygmograph measurement device), which method detects the amount of light absorption that varies in accordance with a change in the volume of an artery caused by a heartbeat (pulse wave).
The photoelectric sphygmograph measurement device projects a fixed amount of light onto a human body, detects remaining light other than the light absorbed by blood, and measures a variation in the remaining light.
As to the photoelectric sphygmograph measurement device, there is a proposal directed to reduction in power consumption and configured to determine whether the measurement of pulse wave is in progress by using the incident level of the light detected and to stop projecting light or decrease the amount of emission of light when the measurement is not in progress (see Japanese Laid-Open Patent Publication No. 1-27532).
However, the proposal have the following issues. The complete stop of the light projection during the time when the measurement of pulse wave is not in progress may consume a long time until it becomes ready for detecting light by the photoelectric element after the measurement of pulse wave is restarted. In the photoelectric element, it may take a long time to accumulate a certain amount of charge.
A similar problem may occur in a case where the measurement of pulse wave becomes possible after a situation in which the photoelectric element is not capable of receiving light continues for a long time.